摘要:

AbstractThe development of large impoundments along the Paraná river, particularly on the Superior section, with fifteen large dams having a capacity over 25000 MW, has had important hydrological and ecological impacts on the lower reaches. The important retention of the suspended solids by the dams has caused a significant reduction of P concentrations. With river impoundment and water eutrophication, cyanophiceae currently dominate during spring and summer, with brief but dense blooms ofAnabaena spiriodesandMicrocystis aeruginosa. Many fishes of the Superior Paraná have been dispersed downstream as the Itaipú reservoir covered the Guayra falls, the natural barrier for these fishes.The most important effects of Superior Paraná dams are related to the changed hydrological regime in the alluvial Middle and Lower reaches. This floodplain plays an important role in the bioproductivity of the river. Fisheries production depends to a high degree on the relationship of the river and its alluvial valley, where the alevines and small fishes of migratory species develop after spawning. During falling river levels the waters carry large quantities of organic matter, floating vegetation, important amounts of plankton and fishes from the alluvial plain to the river. Before the dams, the river defined two subsystems which were joined for about six months during the flood season and effectively isolated during low water periods.Since the commencement of river impoundment and flow regulation, the river ecology has begun a sequence of changes especially within the alluvial reac

ISSN:0886-9375    

DOI:10.1002/rrr.3450040402

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe river Lærdalselva, West Norway, was regulated in the autumn of 1974. Regulation led to an increase in winter flow and a decrease in summer flow in a section where there was natural production of salmon. A slight decrease in summer temperature was also recorded in the uppermost part of this section. No data existed on juvenile Atlantic salmon before regulation and the regulation effect on juvenile fish population parameters is therefore based on samples taken from adult salmon in the period 1969 to 1984.No differences in growth, smolt age, and smolt size which could be related to the regulation of the river were found. The smallest mean sizes of yearlings (0+) were found in 1964 and 1967. After regulation the mean size was never lower than before. Mean smolt age was between 3–1 and 3–9 years, but after regulation never exceeded that found before. River growth was slow, three year old smolts growing faster than four year old smolts. However, there were no differences in river growth before and after regula

ISSN:0886-9375    

DOI:10.1002/rrr.3450040403

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractIn 1986 research divers surveyed and mapped deep‐water spawning redds of fall chinook salmon (Oncorhynchus tshawytscha) in selected sites within an impounded segment of the main‐stem Columbia River, Washington State, U.S.A. In velocities over 3m s−1and depths up to 11 m, two divers riding a manoeuvrable sled made cross‐current transects communicating observations of substrate materials and deep‐water spawning sites. Surface personnel tracked the position of the sled with a laser locating system that logged the information into data storage. Subsequently, the computerized data were translated into overlaying maps depicting location of redds, substrate materials, and depth contours.Deep‐water spawning (>3m) occurred at most survey sites in velocities between 0.6 and 0.8m s−1. The average depth of spawning was 6.5 m, and the maximum was 9.1 m‐deeper than the depth redds can normally be detected by aerial observation (3–4 m). Deep‐water spawning ranged from none to substantial in areas of near identical physical characteristics. A method for estimating abundance and density of deep‐water redds, based upon the data collected with this mapping technique, is presented. This study combined with current limited information concerning deep‐water spawning suggests that up to 80 per cent of the escapement of fall chinook salmon in this reach

ISSN:0886-9375    

DOI:10.1002/rrr.3450040404

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractOrganic and inorganic seston, benthic organic matter and woody debris were studied in a blackwater stream/floodplain system recovering from flow augmentation and thermal discharges. The stream had received cooling waters from two nuclear reactors from the mid‐1950s to 1968, resulting in flows over 10x greater than normal and temperatures that exceeded 70°C. Channel morphology was markedly altered, woody debris was removed or buried, and floodplain vegetation was destroyed. Fifteen years after termination of cooling water discharges, the stream continued to exhibit many characteristics of a disturbed system. Compared to an undistributed reference stream, the recovering stream had substantially less benthic organic matter, fewer snags and debris dams, and transported more organic and inorganic seston of all size fractions examined. Because of the importance of these biophysical factors in the structural morphology of blackwater streams, it is hypothesized that complete recovery will not be realized until the floodplain forest has matured and large woody debris is contributed to the stream chann

ISSN:0886-9375    

DOI:10.1002/rrr.3450040405

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractCutoff bends along modified, stabilized streams often constitute a valuable recreational, ecological, and aesthetic resource. However, their resource value rapidly declines as they fill with sediment, and new cutoff bends do not form to replace them in highly managed rivers.Data from repetitive hydrographic surveys of 20 cutoff bends along four rivers in the southeastern United States were examined using conceptual and analytical models in order to provide a more objective basis for bend management. Bend volume was found to be a log‐decay function of cumulative water discharge through the cutoff reach. Regression analyses were used to generate functions to predict the log‐decay constant. The log‐decay constant varied directly with master stream suspended bed‐material concentration and inversely with variables describing the geometry of the upstream entrance of the old bend. Management of cutoff bends should focus on sequencing construction activities and modification of the upstream bend entrance geometry to reduce the quantity of bed material diverted into the bend. Construction of blockage structures to top‐bank elevation in upstream entrances of cutoff bends is recommended for systems with average suspended bed‐material concentrations greater than about 50ppm. Blockage or modification of entrance geometry of longer bends preserves more aquatic habitat longer than similar levels of effort directed toward shorter bends. Maintenance of a hydraulic connection between the river and at least one end of the cutoff bend is

ISSN:0886-9375    

DOI:10.1002/rrr.3450040406

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe ecological affinity of fish species to different habitat types in the course of their life cycles is investigated in the free‐flowing sections of the Austrian Danube. The results point to the great significance of the degree of hydrological integration between the river and its adjoining waters. In the breeding and fry stage, rheophilic species are bound to the river itself, but the preferred zones show great variations according to both fish age and species. A highly structured shoreline is important in providing a gradient of water current and a spectrum of food sources. Regulated embankments are characterized by an extremely reduced fauna with low population densities of eurytopic species. These results give evidence that the conservation of the characteristic species association is incompatible with the planned hydroelectric power dams in the remaining, free flowing zones of the Danube. The importance of the fish fauna as an indicator group for the condition of large river systems is discussed from the conservation point of vie

ISSN:0886-9375    

DOI:10.1002/rrr.3450040407

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThis communication examines the proposal that actinomycete populations, and thus the occurrence of taste and odour problems in potable water supplies, are related to the input of organic matter to reservoirs. The number of actinomycetes in Lake Mulwala, a man‐made lake in southeastern Australia, ranged from 2–80 ml−1in the water column, and 2.7–12 × 104cm−3in the sediments. Population densities in the water column and sediments were greatest in winter and summer, respectively. They were not highly correlated with protein or polysaccharide degradation. The weak relationship between actinomycete numbers and the rate of organic‐matter breakdown was probably due to metabolic inactivity of the bacteria, since actinomycetes in the sediments occurred mainly as spores rather than as vegetative cells. Limiting the input of organic matter, for instance by the removal of fringing vegetation, will have little effect on actinomycete populations in th

ISSN:0886-9375    

DOI:10.1002/rrr.3450040408

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450040401

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY